One type of cylinder blocks for use in internal combustion engines on automobiles or the like is a closed-deck cylinder block 1 as shown in FIG. 58 of the accompanying drawings. Since the closed-deck cylinder block 1 has a water jacket 2 closed at a gasket surface 3, the closed-deck cylinder block 1 is advantageous in that it is more rigid than open-deck cylinder blocks having a water jacket which is open at a gasket surface.
The closed-deck cylinder block 1 is normally manufactured as follows. First, a cavity is provided by a casting mold, and a collapsible core and highly wear-resistant cylinder sleeves 4 such as FC sleeves, plated sleeves, MMC sleeves, high-silicon-based aluminum sleeves, or the like are placed in the cavity. Then, molten aluminum is poured into the cavity so that it surrounds the collapsible core and the cylinder sleeves 4.
Then, the molten aluminum is cooled and joined in a solid state, producing a block body 5. At this time, the cylinder sleeves 4 are inserted in the block body 5. The cylinder block 1 is now formed wherein the cylinder sleeves 4 are disposed in cylinder bores 6.
The cylinder sleeves 4 and the block body 5 are made of different materials because if the block body 5 is cast of high-silicon-based aluminum, the cylinder bores 6 tends to have defective cavities in their surfaces, often making the cylinder block 1 defective. In addition, since high-silicon-based aluminum is difficult to cut, the cylinder block 1 requires a high machining cost.
Thereafter, the collapsible core is collapsed. A space that is created when the collapsible core is collapsed is used as the water jacket 2. As can be seen from FIG. 58, the water jacket 2 is formed by the removal of a portion of walls between the cylinder bores 6 in the block body 5.
In the closed-deck cylinder block 1 thus manufactured, pistons (not shown) are reciprocally moved in the respective cylinder bores 6. At this time, frictional heat generated by sliding contact between the circumferential side walls of the heads of the pistons and the inner circumferential surfaces of the cylinder sleeves 4 is removed by a coolant that is introduced into the water jacket 2.
In recent years, there have been demands for reducing the amount of fuel, i.e., increasing the mileage of automobiles or the like, for the purpose of preventing global heating. One proposal for meeting such demands is to reduce the weight of internal combustion engines and hence automobiles as final products, as disclosed in Japanese Laid-Open Patent Publication No. 59-3142, Japanese Laid-Open Patent Publication No. 58-74850, Japanese Laid-Open Patent Publication No. 59-79056, and Japanese Laid-Open Patent Publication No. 60-94230.
The weight of the closed-deck cylinder block 1 may be reduced by reducing the volume of the closed-deck cylinder block 1. However, it is difficult to reduce the volume of the closed-deck cylinder block 1 because the wall thickness between the cylinder bores 6 needs to be large enough to accommodate the water jacket 2 between the cylinder bores 6. This drawback manifests itself especially in a multicylinder engine having a plurality of cylinders.
The block body 5 which has a reduced wall thickness may be produced by high-pressure die-casting (HPDC) or precision die-casting. However, the HPDC process makes it difficult to cast the closed-deck cylinder block 1 as it is extremely difficult to employ a core. Therefore the HPDC process is solely used to manufacture open-deck cylinder blocks.
According to the precision die-casting process, if the width of the water jacket 2 is to be reduced, then it is necessary to employ a collapsible core with high-strength and which may be removed easily. However, such a collapsible core is difficult to produce.
In this case, after casting the block body 5, the cylinder sleeves 4 may be inserted into the cylinder bores 6 in the block body 5, and the cylinder sleeves 4 and the block body 5 may be welded to each other. However, this process may cause the block body 5 or the cylinder sleeve 4 to be strained by the heat generated when they are welded to each other. Furthermore, if the block body 5 is manufactured by the HPDC process, then it is difficult to weld the cylinder sleeve 4.
As described above, various difficulties are experienced in manufacturing closed-deck cylinder blocks having small volumes.